Question

The organic compounds P, Q, and R are: 
\(\underline{\hspace{3cm}}\).

• A. P = CH\(_3\)-CH(OH)-CH\(_2\)-CH\(_3\), Q = CH\(_3\)-C(=O)-CH\(_3\), R = CH\(_3\)-C(OH)(CH\(_3\))-CH\(_2\)-CH\(_3\)
• B. P = CH\(_3\)-CH\(_2\)-CH\(_2\)-OH, Q = CH\(_3\)-CH\(_2\)-CHO, R = CH\(_3\)-CH\(_2\)-CH(OH)-CH\(_3\)
• C. P = CH\(_3\)-CH\(_2\)-CH\(_2\)-OH, Q = CH\(_3\)-CH\(_2\)-COOH, R = CH\(_3\)-CH\(_2\)-C(=O)-OCH\(_3\)
• D. P = CH\(_3\)-CH(OH)-CH\(_3\), Q = CH\(_3\)-C(=O)-CH\(_3\), R = CH\(_3\)-CH(OCH\(_3\))-CH\(_3\)

Hint:

In multi-step reaction questions, look for inconsistencies. If you find one, try to identify the most likely typo by checking which parts of the options are chemically sound. Here, the conversion from a corrected Q (butan-2-one) to R (2-methylbutan-2-ol) is a standard Grignard reaction, making the error likely in the provided structure of Q.

Answer 1

The Correct Option is A

Note: There are several inconsistencies and typos in this question as presented.

• The starting material is given as C\(_4\)H\(_{10}\) (butane), which is an alkane and does not undergo hydroboration-oxidation. It should be an alkene, C\(_4\)H\(_8\) (butene).
• In option (A), the structure for Q (acetone) does not result from the oxidation of P (butan-2-ol). Oxidation of butan-2-ol gives butan-2-one.

We will solve the question by assuming the most plausible intended reaction sequence that aligns with the given options. The sequence from P to R is most coherent if we assume a typo in Q.
Step 1: Determining compound P
Let's assume the starting material is an isomer of butene (C\(_4\)H\(_8\)). The reaction is hydroboration-oxidation, which results in the anti-Markovnikov addition of water across the double bond. If we start with but-2-ene (CH\(_3\)-CH=CH-CH\(_3\)), hydroboration-oxidation gives butan-2-ol. P = CH\(_3\)-CH(OH)-CH\(_2\)-CH\(_3\) (Butan-2-ol). This matches the structure of P in option (A).
Step 2: Determining compound Q
Compound P (butan-2-ol, a secondary alcohol) is oxidized with CrO\(_3\) in an anhydrous medium. This reagent oxidizes secondary alcohols to ketones. \[ \text{CH}_3\text{-CH(OH)-CH}_2\text{-CH}_3 \xrightarrow{\text{CrO}_3} \text{CH}_3\text{-C(=O)-CH}_2\text{-CH}_3 \] So, Q should be butan-2-one. Option (A) lists Q as acetone (CH\(_3\)-C(=O)-CH\(_3\)), which is incorrect. This is a likely typo in the question's option. For the sake of finding the "best" answer, let's proceed assuming Q was intended to be butan-2-one.
Step 3: Determining compound R
Compound Q reacts with a Grignard reagent (CH\(_3\)MgBr) followed by acidic hydrolysis (H\(_3\)O\(^+\)). This reaction adds a methyl group to the carbonyl carbon and forms a tertiary alcohol. Assuming Q is butan-2-one: \[ \text{CH}_3\text{-C(=O)-CH}_2\text{-CH}_3 + \text{CH}_3\text{MgBr} \rightarrow \text{CH}_3\text{-C(OMgBr)(CH}_3\text{)-CH}_2\text{-CH}_3 \] Followed by hydrolysis: \[ \text{CH}_3\text{-C(OMgBr)(CH}_3\text{)-CH}_2\text{-CH}_3 \xrightarrow{\text{H}_3\text{O}^+} \text{CH}_3\text{-C(OH)(CH}_3\text{)-CH}_2\text{-CH}_3 \] So, R is 2-methylbutan-2-ol. This structure matches R given in option (A).
Step 4: Final Answer:
Based on the analysis, the reaction sequence that produces P (butan-2-ol) and R (2-methylbutan-2-ol) is consistent if the starting material is but-2-ene and Q is butan-2-one. Option (A) correctly identifies P and R, despite having an error in the structure of Q. It is the most plausible answer among the choices.